Rinse aid compositions designed for use in automatic dishwasher machines are well known. These compositions are added during the rinsing cycle of the machine, separately from the detergent composition employed in the main wash cycle(s). The ability to enhance rinsing, and in particular the ability to prevent spot and film formation are common measures of rinse aid performance.
Rinse aid compositions typically contain components such as nonionic surfactants and/or hydrotropes which aid the wetting of the items in the rinse, thereby improving the efficacy of the rinsing process. These surfactants, and rinse aid compositions in general, are not designed for the achievement of a primary soil removal purpose.
The general problem of the formation of deposits as spots and films on the articles in the wash/rinse, and on the dishwasher machine parts is well known in the art.
Whilst the general problem of deposit formation is known, a full understanding of the many facets of the problem is however still an active area of research.
A range of deposit types can be encountered. The redeposition of soils or the breakdown products thereof, which have previously been removed from the soiled tableware in the washload, provides one deposit type. Insoluble salts such as calcium phosphate or carbonate, calcium fatty acid salts (lime soaps), or certain silicate salts are other common deposit types. Composite deposit types are also common. Indeed, once an initial minor deposit forms it can act as a "seeding centre" for the formation of a larger, possibly composite, deposit structure.
Deposit formation can occur on a range of commonly encountered substrate surfaces including plastic, glass, metal and china surfaces. Certain deposit types however, show a greater propensity to deposit on certain substrates. For example, lime soap deposit formation tends to be a particular problem on plastic substrates.
The formation of insoluble carbonate and phosphate, especially calcium carbonate and phosphate, deposits are a particular problem in the machine dishwashing art. The Applicants have found that the formation of insoluble salt deposits occur most noticeably in the rinse cycle of the dishwasher machine. Deposit build up is most apparent on the heater element of the dishwasher machine.
The Applicants have found that the problem of insoluble salt deposit formation may be effectively ameliorated by the inclusion of amino tricarboxylic acid (ATCA) into a rinse aid formulation.
The Applicants have also found that ATCA can bind magnesium ions reducing the formation of insoluble magnesium salts, such as magnesium silicate on the articles in the wash.
The Applicants have also found that the more effective control of calcium carbonate and phosphate deposition can also lead to benefits in the prevention of the formation of other deposit types, particularly lime soap deposits and silicate deposits.
Lime soap deposits are most commonly encountered when the washload contains fatty soils, which naturally contain levels of free fatty acids, and when lipolytic enzymes are components of the formulation. Lipolytic enzymes catalyse the degradation of fatty soils into free fatty acids and glycerol. Silicate is a common component of machine dishwashing formulations, where it is added for its china care capability.